What Plate current rating do I look for when buying "non Mesa" EL34 tubes for a 3Ch Dual Rectifier or what range would be acceptable to use or what have you used and been ok with? I have found a lot of info on here about matching but nothing specific on plate currents that are acceptable to use for EL34s.
Plate current rating to look for when buying EL34 tubes
- Thread starter gmcelroy
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MusicManJP6
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My Tung Sol EL34Bs are marked '26' i believe.
MusicManJP6
Well-known member
Woops! I told you wrong!! My EL34Bs are marked '36'! It's my KT77s that are marked '24'. Sorry about that!
Old BF Shred
Well-known member
Good question here.
Mesa says the spec for the Stiletto amps is 38-40 ma. idle current.
Likely close to that or the same for a Recto, etc.
It seems many are unclear as to the importance of proper bias and idle current….allow me to try to clarify (on my soapbox, if you will).
In a perfect world you could just order tubes rated for, in this example, 38 or 40 ma. and voila! you’d have the perfect tube set.
In the real world, however, this does not always work.
I have ordered several tubes from Tube Depot, with good luck, so far, so I’ll use them as an example…..
I asked them how they rate their el34’s. They said they measure on a “test amp” (whatever brand, they did not say) that runs 400 volts on plates and -36 volt (bias voltage) on control grid. These values are typical for el34.
My stiletto runs a little higher on both voltages, but is fairly close. To be on the safe side, I usually order them 5-10% lower value…that is I would order 34 – 38 ma. rated tubes.
This comes out OK, maybe a little lower (colder) than the 38-40 Mesa spec.
I have found that it is better to run a little colder than a little hotter. The difference in tone, by running colder, is not as great as the difference in loss of tube longevity, by running hotter, IMHO.
Also, fyi, el34’s can supposedly run as high as 50ma. idling current, but, frankly, I wouldn’t.
If the plates glow red at all, it is too hot (too high idle) or there is another significant problem with the amp causing too much current through the tube. Usually the normal “blue glow” will be noticeably increased as well.
So why not run real cold? Say in the 20’s? Some say this would sound too brittle or harsh, lacking warmth, and while the difference in tone may be subtle, I would not go this low, either. The tubes would likely last a longer time this way, but you may not like the sound at low to moderate volume levels. Why?
Well the theory behind it is that the lower the idle current, the more cross over (the transition from one tube to the other, or from positive to negative waveform in a push pull, class AB or B amplifier) distortion.
This distortion, like the idle current (note the “idle” current, not average current) stays at the same relative level always. As the amp is played louder, this distortion, remaining basically constant, is a lower percentage of the output. When played loud, it is relatively inaudible, compared to the average level coming out the speakers. Make sense? In theory this sounds good, but many people say they can still tell a difference, regardless of volume. I must say I think I can, too, but barely, and not enough of one to sacrifice my “tube budget” over it. So I prefer to use tubes that are a little on “the cold side”.
The bottom line is that the method of rating that various tube suppliers use is likely to vary from one to another, so it may be wise to err on the side of caution and order at slightly colder (lower) ratings until you at least know how that supplier’s ratings hold up in your particular amplifier. I would also make sure to tell them what amp you own as they may have direct experience with your model and help you make an informed decision.
I hope this helps you in making a decision, as it is always a hassle returning the wrong tubes, especially if you got them mail order or on-line.
Good luck!
Mesa says the spec for the Stiletto amps is 38-40 ma. idle current.
Likely close to that or the same for a Recto, etc.
It seems many are unclear as to the importance of proper bias and idle current….allow me to try to clarify (on my soapbox, if you will).
In a perfect world you could just order tubes rated for, in this example, 38 or 40 ma. and voila! you’d have the perfect tube set.
In the real world, however, this does not always work.
I have ordered several tubes from Tube Depot, with good luck, so far, so I’ll use them as an example…..
I asked them how they rate their el34’s. They said they measure on a “test amp” (whatever brand, they did not say) that runs 400 volts on plates and -36 volt (bias voltage) on control grid. These values are typical for el34.
My stiletto runs a little higher on both voltages, but is fairly close. To be on the safe side, I usually order them 5-10% lower value…that is I would order 34 – 38 ma. rated tubes.
This comes out OK, maybe a little lower (colder) than the 38-40 Mesa spec.
I have found that it is better to run a little colder than a little hotter. The difference in tone, by running colder, is not as great as the difference in loss of tube longevity, by running hotter, IMHO.
Also, fyi, el34’s can supposedly run as high as 50ma. idling current, but, frankly, I wouldn’t.
If the plates glow red at all, it is too hot (too high idle) or there is another significant problem with the amp causing too much current through the tube. Usually the normal “blue glow” will be noticeably increased as well.
So why not run real cold? Say in the 20’s? Some say this would sound too brittle or harsh, lacking warmth, and while the difference in tone may be subtle, I would not go this low, either. The tubes would likely last a longer time this way, but you may not like the sound at low to moderate volume levels. Why?
Well the theory behind it is that the lower the idle current, the more cross over (the transition from one tube to the other, or from positive to negative waveform in a push pull, class AB or B amplifier) distortion.
This distortion, like the idle current (note the “idle” current, not average current) stays at the same relative level always. As the amp is played louder, this distortion, remaining basically constant, is a lower percentage of the output. When played loud, it is relatively inaudible, compared to the average level coming out the speakers. Make sense? In theory this sounds good, but many people say they can still tell a difference, regardless of volume. I must say I think I can, too, but barely, and not enough of one to sacrifice my “tube budget” over it. So I prefer to use tubes that are a little on “the cold side”.
The bottom line is that the method of rating that various tube suppliers use is likely to vary from one to another, so it may be wise to err on the side of caution and order at slightly colder (lower) ratings until you at least know how that supplier’s ratings hold up in your particular amplifier. I would also make sure to tell them what amp you own as they may have direct experience with your model and help you make an informed decision.
I hope this helps you in making a decision, as it is always a hassle returning the wrong tubes, especially if you got them mail order or on-line.
Good luck!
That was very good info Old BF Shred! I went ahead and placed the EL34's into the amp and have had them in for about 5 days now and have not noticed anything out of the ordinary. I bought the tubes with the intent to use them in my Marshall DSL100 when I had it repaired a month back. I contacted the tech and asked about running them and he said that they should be fine in the Mesa. He made the comment that when he orders EL34's he specifically requests the draw to be in somewhere between 30 to 42, which works well in most EL34 based amps without overheating and is generally a "safe" range.
Old BF Shred
Well-known member
Great!
I presume these are the SED wing C's rated at 38?
That should be just about right. Even if its a few percent higher or lower, it's well within range for the el34 and should work and sound fine.
Good luck and Happy Holidays!
I presume these are the SED wing C's rated at 38?
That should be just about right. Even if its a few percent higher or lower, it's well within range for the el34 and should work and sound fine.
Good luck and Happy Holidays!
Alot of good info here, but let me add ......
There is more to it than just cathode current. Sure that is an important value, but there is more to it.
Bias is the amout of idle plate dissipation. The general rule is to run no less than 50% and no more than 70%. To find that % of plate dissipation you need to know both the cathode current and plate voltage.
For example, a 6L6GC is rated at 30 watts maximum plate dissipation (EL34's are 25W MPD). I will usually run my 6L6GC's around 55-60% of max plate dissipation, for approx. 16.5-18 watts dissipation at idle.
My Roadster runs about 470 volts on the plate in Bold/SS. At 36mA of measured cathode current, thats right about 56% idle dissipation using the formula Plate Volts * mA = watts (470[v]*0.036[mA]=16.9[w]). 16.9 watts is 56.4% of 30 watts.
If the plate voltage was 400V, that 36 mA would only be 14.4 watts, or 48% max dissipation.
Just my $0.02
Dom
There is more to it than just cathode current. Sure that is an important value, but there is more to it.
Bias is the amout of idle plate dissipation. The general rule is to run no less than 50% and no more than 70%. To find that % of plate dissipation you need to know both the cathode current and plate voltage.
For example, a 6L6GC is rated at 30 watts maximum plate dissipation (EL34's are 25W MPD). I will usually run my 6L6GC's around 55-60% of max plate dissipation, for approx. 16.5-18 watts dissipation at idle.
My Roadster runs about 470 volts on the plate in Bold/SS. At 36mA of measured cathode current, thats right about 56% idle dissipation using the formula Plate Volts * mA = watts (470[v]*0.036[mA]=16.9[w]). 16.9 watts is 56.4% of 30 watts.
If the plate voltage was 400V, that 36 mA would only be 14.4 watts, or 48% max dissipation.
Just my $0.02
Dom
Old BF Shred
Well-known member
Dom, are you reading 470v with a tube in the socket? My stiletto (and 50/50, too) will read much higher without tubes in the socket, but only about 410-415 with them in.
You are correct that 6L6 specs 30 w plate dissipation (per Raytheon tube manual).
Your math certainly looks to be in line with what most amps run at (that I've seen). And especially given that cathode current is the sum of plate and screen current, it may seem we all tend to run our amps too cold. However.....
What I find interesting is that I have checked the waveform (on a scope) of many amps I've set up for friends and the visible step that represents crossover distortion usually disappears long before (lower than...some as low as 15-20 ma.) the idle current reaching expected "nominal & normal" value for the given output tube.
BUT that does not mean you can't hear a difference. I am only saying that you may find your tubes will last longer if you go easier "on the throttle", so to speak.
Either way, it basically boils down to what we find to be personal preference; whatever works out well for you is what counts!
Take care and Happy Holidays!
You are correct that 6L6 specs 30 w plate dissipation (per Raytheon tube manual).
Your math certainly looks to be in line with what most amps run at (that I've seen). And especially given that cathode current is the sum of plate and screen current, it may seem we all tend to run our amps too cold. However.....
What I find interesting is that I have checked the waveform (on a scope) of many amps I've set up for friends and the visible step that represents crossover distortion usually disappears long before (lower than...some as low as 15-20 ma.) the idle current reaching expected "nominal & normal" value for the given output tube.
BUT that does not mean you can't hear a difference. I am only saying that you may find your tubes will last longer if you go easier "on the throttle", so to speak.
Either way, it basically boils down to what we find to be personal preference; whatever works out well for you is what counts!
Take care and Happy Holidays!
Looking for the "crossover notch" on a scope is not the best way to find the bias point.I've seen a MKIV with the EL34's running at 8ma's and showed no crossover notch on the scope,and it didnt sound terrible,not the best,but still not terrible.That is why it is best to set the bias "by ear",or to use the numbers i.e. 70% of max. and dial in from there.As for tube life at higher current draw,it all depends on the tube.An amp I built for my son has a pair of NOS GEC Kt66's running about 375 volts at 62 ma's,for the last 3 years,3-5 nights a week,I just gave the amp a check-up about 2 weeks ago and still dont need to change the tubes yet,they sound great and still test the same as they did 3 years ago on my testers.So if you like it a little hotter,go for it,I mean,how much longer could those tubes last at 70%?Mesa sets their bias point quite cold,so it is rare that you find a set that will be too hot in any of their amps,so if you arent able to re-set the bias in your Mesa amp,if you just watch the plates and they arent redplating,you are good to go.
Old BF Shred
Well-known member
Hi Stokes.....
On that, I do agree. I have run "bias" down to this point and I can hear a real difference regardless what the scope shows;from 10 or 15 ma to say, 30 ma. is very discernable. Going from 30 to 40; not so much.
I think you hit the nail on the head.....NOS.....I have had older american made tubes (RCA, some GE) that I have used in the past and they never gave me any grief...seemed to last forever...in fact, some I still have.
These newer tubes don't seem to take any "pushing" (I won't even say 'abuse').
like the old ones. Yes, Mesa does seem to run them cold.....that way they minimize tube replacement issues during warranty (I'd imagine).
And despite what Mesa claims, there are tubes out there that sound better than their own, and many cost less (e.g. JJ, Mullard reissue, NOS! ...).
What I have found, and again, this is just what I've noticed, is that when running the tubes a bit colder, it seems to take longer for the amp "to come to temperature". I mean, notice how when you've been playing a while and when the amp is good and hot how it sounds better than when you first started playing? This time period seems to be longer with colder biasing.
But in time that "gap" seems to close, at least somewhat (to my ears, anyway, but hey, I'm deaf in one ear and can't hear out the other :lol: ).
I have put adjustable biasing in my 50/50 and can experiment with that. Since my Ace is still under warranty (and at the moment, STILL in the shop...another story), I'll have to wait to do it to that one.
I have never seen red plates on my 50/50 so far, but have on other amps....it's not a pretty sight (for long).
Thanks for the info here, Stokes...good stuff!
I hope you have a great Christmas and New Year.
Take care!
On that, I do agree. I have run "bias" down to this point and I can hear a real difference regardless what the scope shows;from 10 or 15 ma to say, 30 ma. is very discernable. Going from 30 to 40; not so much.
I think you hit the nail on the head.....NOS.....I have had older american made tubes (RCA, some GE) that I have used in the past and they never gave me any grief...seemed to last forever...in fact, some I still have.
These newer tubes don't seem to take any "pushing" (I won't even say 'abuse').
like the old ones. Yes, Mesa does seem to run them cold.....that way they minimize tube replacement issues during warranty (I'd imagine).
And despite what Mesa claims, there are tubes out there that sound better than their own, and many cost less (e.g. JJ, Mullard reissue, NOS!
...).What I have found, and again, this is just what I've noticed, is that when running the tubes a bit colder, it seems to take longer for the amp "to come to temperature". I mean, notice how when you've been playing a while and when the amp is good and hot how it sounds better than when you first started playing? This time period seems to be longer with colder biasing.
But in time that "gap" seems to close, at least somewhat (to my ears, anyway, but hey, I'm deaf in one ear and can't hear out the other :lol: ).
I have put adjustable biasing in my 50/50 and can experiment with that. Since my Ace is still under warranty (and at the moment, STILL in the shop...another story), I'll have to wait to do it to that one.
I have never seen red plates on my 50/50 so far, but have on other amps....it's not a pretty sight (for long).
Thanks for the info here, Stokes...good stuff!
I hope you have a great Christmas and New Year.
Take care!
Southernhell
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I understand what has been said in this thread, but wouldn't it be easier for those of us that want to try and find OTM(other than Mesa) power tubes would be to find what the B+ voltage is on the amp, then start looking for the tubes?
Most tube resellers rate their tubes using 400V, but guitar amps usually run closer to the 500v mark don't they? Using tubes rated at 400v would require some interesting math equations to find out if they would in fact work within the 60-70% max plate dissipation one usually biases their tubes to. Are Mesa amps different in this aspect though?
I ask as I have been told that running EL34's on a Dual Rec(like what I own) without using the tube rectification may damage the amp. You use the tube rectifier to bring down the plate voltage heading to the power tubes so there is no problem.
This is one question I have not seen answered here or elsewhere. What equations are people using, including Mesa to come up with what you want your amp biased to. I can do the math for adjustable bias amplifiers, but are the same equations used on Mesa's?
Most tube resellers rate their tubes using 400V, but guitar amps usually run closer to the 500v mark don't they? Using tubes rated at 400v would require some interesting math equations to find out if they would in fact work within the 60-70% max plate dissipation one usually biases their tubes to. Are Mesa amps different in this aspect though?
I ask as I have been told that running EL34's on a Dual Rec(like what I own) without using the tube rectification may damage the amp. You use the tube rectifier to bring down the plate voltage heading to the power tubes so there is no problem.
This is one question I have not seen answered here or elsewhere. What equations are people using, including Mesa to come up with what you want your amp biased to. I can do the math for adjustable bias amplifiers, but are the same equations used on Mesa's?
There is more to it than merely knowing the plate voltage.And even tho Mesa are "fixed bias" that doesnt mean they arent adjustable."Fixed" means there is a fixed negative voltage applied to the control grid.I dont understand what you mean by using equations to come up with what you want your amp biased to.Mesa sets the negative voltages in their bias supply then tests tubes that will fall into a safe bias range in their amps.It is not like you can just pick a tube and know,using equations or not,what they will bias at.They have to be put in the circuit and take the required measurements (plate volts,current draw).Southernhell said:
Southernhell
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I menat using ohms law equations for calculating correct plate dissipation of the tubes within the circuit. sorry if I didn't make that clear. I know that it takes more than knowing the plate voltage for the amp.
Cathode Current = Cathode Voltage/Cathode Resistor Value (Ohms)
Screen Current = Voltage Drop across Screen Resistor/Screen Resistor Value (Ohms)
Plate current = Cathode Voltage/Cathode Resistor Value (Ohms) - Screen Current
Plate Dissipation in Watts = (Plate Voltage - Cathode Voltage) x Plate Current
or
Replace the ground wire on each power tube socket with a 1-ohm resistor.
Read the voltage drop across this resistor (in millivolts) with your DMM.
Read the plate voltage.
Use the above readings to calculate the static dissipation wattage.
Adjust the bias to obtain the best tone, while keeping the tubes within specifications.
What I was implying was that when you order tubes for a non-Mesa amp, you are usually asked what your B+ is, so that they can get you into a ballpark reading of tubes that will bias correctly within your amps current draw. Once you know this you can order tubes that will put you into the "desired" 60-70%TPD. Usually if you order EL34's they will spec out, though you can order hotter tubes. Same with 6L6's.
What I think the OP was referring to was how are we to order tubes for your Mesa when you want to achieve the 60-70%PD when its a fixed bias amp that is biased cold from the factory. Personally I went to Mesa because I like the drop and go aspect of the tubes. I played Marshalls for almost 20 years and biasing at times was a PITA, esp when you are using a pcb amp and swapping from EL34's to E34L's to 6650's to KT88's resulted in times having to swap out bias resistors, and or trimmers. Maybe a detailed explanation from some of the more technical members here could provide a how-to guide(including pictures) for those that would want to re-bias their respective amp to run at 60-70%PD using any given set of tubes, ratings aside. I know I love the way my amp sounds now, just wonder sometimes how much better it would sound with power tubes properly biased for those tubes and not within a relatively loose spec.
I know that you can take out the bias resistor to adjust the bias of a Mesa. Kind of a big pain in the ass when you will have to do it almost everytime you retube and you decide to swap out tube brands. If Mesa's were PTP amps, this wouldnt be a problem, but since they are on PCB's you run the risk of a lifted pad after so many years. Would be easier if they would have installed a trimmer in line with the bias resistor, but I understand Mesa's thinking on this.
Hope this clarified my previous post.
Cathode Current = Cathode Voltage/Cathode Resistor Value (Ohms)
Screen Current = Voltage Drop across Screen Resistor/Screen Resistor Value (Ohms)
Plate current = Cathode Voltage/Cathode Resistor Value (Ohms) - Screen Current
Plate Dissipation in Watts = (Plate Voltage - Cathode Voltage) x Plate Current
or
Replace the ground wire on each power tube socket with a 1-ohm resistor.
Read the voltage drop across this resistor (in millivolts) with your DMM.
Read the plate voltage.
Use the above readings to calculate the static dissipation wattage.
Adjust the bias to obtain the best tone, while keeping the tubes within specifications.
What I was implying was that when you order tubes for a non-Mesa amp, you are usually asked what your B+ is, so that they can get you into a ballpark reading of tubes that will bias correctly within your amps current draw. Once you know this you can order tubes that will put you into the "desired" 60-70%TPD. Usually if you order EL34's they will spec out, though you can order hotter tubes. Same with 6L6's.
What I think the OP was referring to was how are we to order tubes for your Mesa when you want to achieve the 60-70%PD when its a fixed bias amp that is biased cold from the factory. Personally I went to Mesa because I like the drop and go aspect of the tubes. I played Marshalls for almost 20 years and biasing at times was a PITA, esp when you are using a pcb amp and swapping from EL34's to E34L's to 6650's to KT88's resulted in times having to swap out bias resistors, and or trimmers. Maybe a detailed explanation from some of the more technical members here could provide a how-to guide(including pictures) for those that would want to re-bias their respective amp to run at 60-70%PD using any given set of tubes, ratings aside. I know I love the way my amp sounds now, just wonder sometimes how much better it would sound with power tubes properly biased for those tubes and not within a relatively loose spec.
I know that you can take out the bias resistor to adjust the bias of a Mesa. Kind of a big pain in the ass when you will have to do it almost everytime you retube and you decide to swap out tube brands. If Mesa's were PTP amps, this wouldnt be a problem, but since they are on PCB's you run the risk of a lifted pad after so many years. Would be easier if they would have installed a trimmer in line with the bias resistor, but I understand Mesa's thinking on this.
Hope this clarified my previous post.
No need to replace the resistor every time,just replace it once with a trim pot.If a supplier asks "what your B+ is" to get you tubes to"match" anything,find another supplier.That wont tell you anything.If my amp has 400 B+ volts and your amp has 400 B+ volts,but mine has -40 v's on the control grid and yours has -30 on the control grid,what is he matching?For those who,as you say,want to re-bias their amp to run at 60-70% using any set of tubes,you must mod the amp to have an adjustable bias set up,a trim pot.Very easy to do,but if you need step by step,including pictures,it is best to leave it to a tech.Not meaning to sound condescending,but there are serious voltages in an amp,and if you dont know what you are touching,you could get hurt,or killed or do serious damage to the amp.
gmcelroy said:
Most tube stores will help you get mesa "spec'd tubes .
Here is the GT to mesa spec chart .
The bottom line here is;
Lower numbers will start to distort at lower volume settings on your amp, and have more dynamic touch and feel.
These are the GT 1-3 range, and the Fender "blue" painted tubes. Many Jazz or Blues players like this range, and
they work well for recording where levels are going to be lower, or in smaller venues.
Medium numbers are the most versatile, will drop into most amps and be very close to most factories bias settings,
and are the best general choice for most players wanting a versatile well rounded amp. These are the GT 4-7
range, and the Fender "white" painted tubes. The range of 4,5,6 are able to be used in Mesa Boogie fixed bias
amps, and on the Mesa scale convert roughly to:
Mesa scale Groove Tubes scale
Red 4
Yellow 4
Green 5
Gray 5
Blue 6
White 6
Nice to keep handy
/cheers
fishyfishfish
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So, not to interrupt, but when I get of set of EL34L's that say 28, they mean 28 Ma's, and if that is correct, would it only apply to an amp with 400 plate volts?
